Bituminous materials, such as bituminous binders, asphalt, coal tar pitches, and petroleum residue, whether of natural or synthetic origin, are used in many construction and industrial applications, such as roofing, waterproofing, and, in particular, the paving of roadways, parking lots, and the like. In paving applications, a hot asphalt mix typically is produced at an asphalt processing plant and is transported to the construction site in a vehicle, e.g., a truck, such as a dump truck, equipped with a metal bed or other container, such as a trailer. Once the asphalt is transported to the construction site, the asphalt is discharged from the truck bed or trailer and is applied to existing asphalt pavement or a rock or concrete base using paving equipment, such as an asphalt spreader and a pressure roller, coupled with the use of manual workpieces, such as shovels, rakes, and other tools.
The same properties that give bituminous binders and asphalt their desirable characteristics, for example, toughness and outstanding adhesion to a variety of substrates, can present significant problems in the course of their use in paving and other applications. For example, the asphalt can adhere to the metal surfaces, such as the truck beds, paving equipment, and workpieces, with which it comes into contact. Such problems have been exacerbated by the recent introduction of new types of asphalt compositions that are modified with organic polymeric materials, such as synthetic or natural rubbers, thermoplastic elastomers, and thermoplastic resins, which tend to form more tenacious bonds with a variety of materials and substrates.
The adhesion and buildup of bituminous materials on paving equipment has long been problematic. The tendency of asphalt to adhere to the metal surface of the truck bed, for example, prevents the asphalt from smoothly sliding out of the bed as the truck attempts to discharge its load. In such circumstances, workers must manually coax the residual asphalt out of the truck bed, exposing workers to hot asphalt that can contain hazardous petroleum-based chemicals. Solidified pieces of asphalt often adhere to the bed despite the workers' best efforts. Thus, asphalt is wasted and material usage suffers. Also, as the hardened deposits of asphalt build up on the surface of the truck bed, the deposits can eventually break off as large solid inclusions in subsequent road mixes, thereby degrading the quality of the applied product. Further, adhesion of residual asphalt to the paving equipment and workpieces often renders the paving equipment and workpieces unsuitable for their intended purposes and causes cleanup and maintenance problems.
Thus, in an effort to circumvent the aforementioned problems which occur during the transport and handling of hot-mix asphalt, it has been necessary to treat the surfaces of the truck bed, paving equipment, and workpieces with a suitable release agent to prevent the asphalt mix from adhering to the metal surfaces thereof. In the past, petroleum oils, such as diesel fuel (or a similar type of petroleum-based fuel), have been used to coat the walls of the truck beds or trailers to facilitate asphalt release. The use of diesel fuel-based release agents, however, has largely fallen into disfavor for several reasons. First, the indiscriminate use of diesel fuel as a release agent can contaminate the soil and ground water, leading to heightened environmental concerns. Accordingly, the U.S. Department of Transportation and many state highway departments have restricted the use of diesel fuel as a release agent. Second, the use of diesel fuel presents a health risk to workers exposed to the diesel fuel during application. Third, diesel fuel is flammable and thus poses a safety risk when used in the proximity of hot asphalt production or paving equipment. Fourth, the release capabilities of diesel fuel decrease over time, for example, during lengthy trips from the asphalt source to the paving project. Finally, diesel fuel-based release agents often act as a solvent to dilute or “cut” the asphalt, thereby degrading the structural integrity of the applied asphalt product. For example, diesel fuel has a tendency to migrate to the surface of the pavement, which results in the formation of soft spots in the pavement. Further, diesel-fuel based release agents are not always effective in promoting the release of polymer-modified asphalt compositions from metal substrates.
Other asphalt release agents known in the art often contain components, such as vegetable oils and animal fats, which also tend to dissolve, and thereby soften, the asphalt material. Although vegetable oils and animal fats are less damaging to the asphalt in this regard than diesel fuel-based release agents, they can still strip bituminous binders from the hot-mix asphalt at the elevated temperatures commonly observed in paving applications and thereby compromise the integrity of the applied product. Most of these release agents also suffer from other undesirable characteristics, such as being environmentally hazardous, thermally unstable, corrosive, prohibitively expensive, and/or of limited effectiveness. Also, the delivery, preparation, and application of these release agents often can be complex. Further, these release agents often require frequent applications to promote satisfactory release of the asphalt from the substrate.
Another approach to solving this problem has been to use water-soluble compositions as asphalt release agents. The use of water-based compositions is attractive because, as opposed to volatile organic solvents, water is environmentally benign and relatively inexpensive. One drawback to this approach, however, is that, due to the low viscosity of water and many aqueous solutions, the film rapidly drains off of the substrate, thereby leaving the substrate unprotected. Thus, the aqueous film does not adhere to the substrate for a sufficient amount of time to prevent adhesion of the asphalt to the substrate.
A further desired characteristic for commercially acceptable asphalt release agents is that they must be suitable for use shortly after application to a substrate. Accordingly, compositions that provide effective release only after extended drying periods are not suitable for use as asphalt release compositions in paving applications. The requirement of extended drying periods is another potential drawback to the use of water-based compositions due to the much slower evaporation of water as compared to volatile organic solvents. Further, the formation of stable aqueous emulsions of suitable release agents, such as polysiloxanes, can be difficult to achieve.
Therefore, there is a long-felt need for an improved asphalt release agent, in particular a water-based composition, which is effective in promoting the release of bituminous materials, such as asphalt, from a substrate; is environmentally safe, non-toxic, and biodegradable; does not degrade or compromise the integrity of the asphalt product; adheres sufficiently to the substrate to which it is applied; and provides for multiple releases of the bituminous material from the substrate.
Other desirable characteristics in an asphalt release agent would include: the capability to be applied without the use of volatile organic solvents and/or specialized equipment; the ability to inhibit the corrosion of the surfaces to which is applied; thermally stability, so it will not decompose and/or volatilize when contacted with the hot asphalt mix; the ability to inhibit the growth of living organisms during storage; and a sufficiently high flash point to avoid flammability hazards which might be encountered at the asphalt source or paving site. Moreover, the release agent should be easy to prepare, deliver and apply even in cold weather conditions. Also, because of the large surface areas to be coated and the frequency of the required coatings, the release agent composition should be relatively inexpensive to produce and apply.
Further, the release composition should be effective for use with different types of bituminous materials, including but not limited to, hot bitumens, bituminous binders, bitumen sheets, coal tar pitches, special-purpose coal tar pitches and formulations comprising special-purpose coal tar pitches, and, various types of asphalts, such as silent (rubberized) asphalts, polymer-modified asphalts, water-permeable asphalts, abrasion resistant asphalts, colored asphalts, and high-viscosity asphalts.
Accordingly, the presently disclosed subject matter was discovered to fill the need for an improved release composition and methods of use thereof for promoting the release of bituminous materials and other adhesive materials from a substrate.